1. Field of the Invention
The present invention relates to retarded acid soluble magnesium oxychloride cement compositions and methods of utilizing such compositions for temporarily plugging or sealing subterranean zones.
2. Description of the Prior Art
In the drilling and completion of well bores penetrating subterranean formations containing hydrocarbons, voids and other highly permeable zones within the formations are often encountered. Such zones can cause a variety of problems including the loss of expensive drilling or completion fluids thereinto. Heretofore, lost circulation treatments involving various plugging materials such as walnut hulls, mica and cellophane have been used to prevent or lessen the loss of fluids from well bores. The disadvantages of such treatments include the potential for damage to hydrocarbon bearing formations as a result of the inability to remove the plugging materials therefrom, and the dislodgement of the plugging materials from highly permeable zones whereby fluid losses subsequently resume.
A more preferred technique for preventing lost circulation problems has been to temporarily plug voids or permeable zones with magnesium oxychloride cement compositions. Solid magnesium oxychloride cements can be removed with minimal damage to hydrocarbon bearing zones or formations by dissolution in acids. However, prior set retarded magnesium oxychloride cement compositions utilized in well drilling and completion applications have had relatively short thickening times, particularly at temperatures approaching 220.degree. F. As a result, prior retarded magnesium oxychloride cement compositions often can not be placed in a deep and/or hot subterranean zone before becoming too thick to pump.
Thus, there is a need for improved retarded acid soluble magnesium oxychloride cement compositions and methods whereby removable plugs or seals can be formed in relatively deep and/or hot subterranean zones therewith.